Strengthening of headstocks with vertical clamping to enhance shear capacity

Abstract

Deteriorated bridges all around the world are in need of replacement, or repair and strengthening. This damage is commonly caused by the overloading of bridges, due to the increasing size of heavy vehicles using the bridges today. Full bridge replacement poses the problems of high cost and disruption to traffic, so suitable methods of repair and strengthening are required. A common deterioration of these bridges is shear cracking. External vertical clamping is a method of shear strengthening girders, but existing shear cracks can limit the effectiveness of the external vertical clamping. Epoxy injection is a method of structurally repairing cracks, which could possibly be used to repair the shear cracks. If effective, this would allow the vertical clamping to effectively strengthen the member. This project is studying the shear strengthening of concrete girders using external vertical clamping, with existing shear cracks repaired with epoxy injection. This research investigates the combined repair method with experimental testing of four rectangular beams. Three of the beams were preloaded to form shear cracks, with the other strengthened only with vertical clamping. After vertical clamping all of these beams were loaded until ultimate failure. The results from these beams were compared to a reinforced control beam, and a vertical clamped control beam. These comparisons were made to evaluate the effectiveness of the combined repair method. 2The results from this testing indicate that applying vertical clamping alone to a shear cracked girder will increase the member’s capacity, however the existing shear cracks cause the ultimate shear strength to reduce if un-repaired. The testing also shows that by combining external vertical clamping with epoxy injection of the existing cracks, a deteriorated girder will have a significant increase in shear capacity. Hence, this combined rehabilitation technique has been shown to be an effective method of shear strengthening.